The operation of certain computer equipment can be negatively affected by the presence of environmental hazards, such as airborne contaminants. To prevent this harm from occurring, some sensitive equipment may be housed in an enclosure that is designed to keep out airborne contaminants.
An example of a piece of sensitive equipment housed within a protective enclosure is a hard-disk drive (HDD). An HDD is a non-volatile storage device, which is housed in a protective enclosure, that stores digitally encoded data on one or more circular platters having magnetic surfaces. When an HDD is in operation, each platter is rapidly rotated by a spindle system. Data is read from and written to a platter using a read/write head which is positioned over a specific location on a platter by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a platter. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the space between a read/write head and the surface of a platter must be tightly controlled. To provide a uniform distance between a read/write head and the surface of a platter, an actuator relies on air generated by a self-acting air bearing to support the read/write heads at the proper distance away from the surface of a platter while the platter rotates. A read/write head therefore is said to “fly” over the surface of a platter. That is, the air pulled along by a spinning platter forces the head away from the surface of the platter. When a platter stops spinning, a read/write head must either “land” on the platters or be pulled away.
Very small airborne particles, such as the size of 10 nm to 1000 nm (1 micron), may adhere to the air bearing surfaces of either a read/write head or deposit on the surface of the magnetic platters (disk stack). When the surface of either a read/write head or a platter becomes attached to airborne particles, it is more likely that a read/write head may not read data properly or may scrape across the surface of a platter, which could grind away the thin magnetic film of the platter and cause data loss and potentially render the HDD inoperable.
It may be necessary to equalize the pressure between the interior and the exterior of the HDD in certain situations, such as when the hard-disk drive is turned on or turned off, when the HDD is brought to a different elevation (e.g., from sea level to a mountain top), or when the temperature of the HDD is much different than the ambient temperature. To equalize the pressure between the interior and the exterior of the enclosure, the enclosure has a small opening (an “air passage”) located in the cover of the HDD that allows air to travel between the interior and the exterior of the enclosure. The air passage is covered by a filter (referred to as a “breather filter”) that filters the air to prevent any airborne particles outside of the enclosure from entering the interior of the enclosure. When the hard-disk drive is in a steady state (i.e., after it has been turned on or off for a period of time), there should be no air flow through the air passage covered by the breather filter, although mass diffusion will still occur.